from __future__ import annotations

from dataclasses import dataclass


@dataclass
class BearingRope:
    required_breaking_kN: float
    initial_tension_kN: float
    note: str


def select_bearing_rope(span_m: float, design_load_kN: float, material: str = "HMPE", safety_factor: float = 3.0, initial_tension_ratio: float = 0.25) -> BearingRope:
    """承力索选型（迪尼玛或钢绳）：破断拉力≥载荷×SF；初张力为比例。"""

    return BearingRope(required_breaking_kN=design_load_kN * safety_factor, initial_tension_kN=design_load_kN * initial_tension_ratio, note=f"材料:{material}")


